1. Field of the Invention
The present invention relates to a resist composition used suitably in ultramicrolithography and other photofabrication processes for producing VLSI circuits, high-capacity microchips and the like, and further relates to a pattern formation method using such a resist composition. More specifically, the invention is concerned with a resist composition capable of forming superfine patterns through application of KrF excimer laser light, electron beams, EUV rays or the like, and with a pattern forming method using such a resist composition. In other words, the invention relates to a resist composition and a pattern formation method using this composition, which are suitable for use in super minute patterning of semiconductor elements by means of KrF excimer laser light, electron beams or EUV rays.
2. Description of the Related Art
In fabrication processes of semiconductor devices, such as ICs and LSI circuits, fine patterning by lithography using photoresist compositions has so far been carried out. With recent increase in packing densities of IC chips, formation of super minute patters in the submicron or quarter-micron region has come to be required; consequently, there has been a trend for the exposure wavelengths to be made shorter, from the g-ray to the i-ray and further to KrF excimer laser light. Besides using KrF laser light, development of lithography using electron beams, X-rays or EUV rays is also being pursued at present.
Lithography using electron beams or EUV rays is ranked as the next generation or after-the-next generation of pattern formation technology, and high-sensitivity, high-resolution resists suitable for such lithography are being expected. Although enhancement of sensitivity is a very important problem in aiming reduction of a wafer processing time in particular, pursuit of increase in sensitivity of positive-working resist for electron-beam or EUV use causes not only lowering of resolution but also degradation in line width roughness (LWR). Therefore, development of resist satisfying these properties at the same time is intensely to be desired. Since high sensitivity and high resolution bear a tradeoff relationship to satisfactory LWR, the problem of how to satisfy them at the same time becomes highly important.
In lithography using KrF laser light, as in the above case, simultaneous attainment of high sensitivity, high resolution and satisfactory LWR is a significant challenge, and besides, there occur problems of standing waves and line-width swings (abbreviated to swings or SW) resulting from variations in thickness of resist film on a highly reflective substrate typifying an ion implantation process. In the case of using a highly reflective substrate, there is a trend for swings resulting from variations in resist film thickness to become wide when the resist has a high transmittance, and it is known that they are reduced by introduction of dyes. However, the introduction of dyes causes lowering of resolution and degradation in LWR, and besides, there may be cases where a baking plate is polluted with dyes subliming at the baking step in the process of resist film formation. So, how to resolve those problems at the same time is of great significance.
As resists suitable for the lithographic processes using KrF excimer laser light, electron beams or EUV rays, chemical amplification resists utilizing acid catalysts are chiefly used from the viewpoint of increasing the sensitivity. As to those of positive-working type, chemical amplification resist compositions containing phenolic polymers having properties of being insoluble or slightly soluble in alkali developers and turning soluble in alkali developers under the action of acids (hereafter abbreviated as “acid-decomposable phenolic resin”) and acid generators as main components are effectively used.
One example of chemical amplification positive-working resist compositions in the nascent stages, which each contain a photo-acid generator and a resin protected by acid-decomposable groups, is disclosed in U.S. Pat. No. 4,491,628. Such a chemical amplification positive-working resist composition is a pattern-forming material which can form patterns on a substrate by undergoing exposure to radiation, such as far-ultraviolet rays, to produce an acid in exposed portions and causing the acid-catalyzed reaction therein to bring about variations in developer solubility between the portions irradiated and unirradiated with the active radiation.
Various positive-working resist compositions of the type which contain resins protected by acid-decomposable groups have so far been known. For example, the resist composition using a poly(hydroxystyrene) resin protected by alkoxy (acetal) groups is disclosed in JP-A-5-249682, the resist composition using a poly(hydroxystyrene) resin protected by two different kinds of acid-decomposable groups in JP-A-9-211866, the resist composition using a resin protected by acetal groups having heterocyclic groups at their respective ends via linkage groups in JP-A-2000-352822, the resist composition using a poly(hydroxystyrene) resin protected by two different kinds of acetal groups in JP-A-2002-49156, the resist composition using an anthracene ring-containing substance as dye in JP-A-2004-302434, and the hydroxystyrene units having substituents in JP-A-2005-352337, but in actuality none of those combinations can satisfy all the requirements described above at the same time, namely all of high sensitivity, high resolution and satisfactory LWR in the super minute region, and reductions in standing waves and swings resulting from variations in resist film thickness on a highly reflective substrate, which is representative of the KrF ion implantation process.